Extrusion methods



Aug 2, 1966 R. Nn-:ssNr-:R ETAL 3,264,383

EXTRUSION METHODS Original Filed Feb. 23, 1962 4 Sheets-Sheet l Aug. 2, 1966 R. NIESSNER ETAL` 4 Sheets-Sheet 2 Filed Feb. 25, 1962 Aug. 2, 1966 R. Nlr-:ssNER ETAL.

ExTRusIoN METHODS original Filed Feb. 23, 1962 4 Sheets-Sheet 5 n @Paw mm Aug. 2, 1966 R. NlEssNER ETAL EXTRUSION METHODS 4 Sheets-Sheet 4 Original Filed Feb. 25. 1962 QN l United States Patent: Office.

3,254,383 Patented August 2, 1966 3,264,383 EXTRUSION METHODS Rudolf Niessner, Bogen, Max Sonnletner, Oberaltaich, near Bogen, Karl Hermann Wolf, Regenhutte, near Zwiesel, and Johann Gutlhuber, Irlbach, near Straubing, Germany, assignors to Kunstolwerk Gebruder Anger G.m.b.H. & Co., Munich, Germany, a firm Original application Feb. 23, 1962, Ser. No. 176,179, now Patent No. 3,205,535, dated Sept. 14, 1965. Divided and this application Aug. 28, 1963, Ser. No. 310,186 Claims priority, application Germany, Feb. 25, 1961, K 43,015; Nov. 22, 1961, K 45,267 11 Claims. (Cl. 264-95) This is a division of application Serial No. 176,179, filed February 23, 1962, now Patent No. 3,205,535.

This invention relates to processes for the production of extruded tubes, with widenings and/ or thickenings extending transversely Ito the direction of discharge of extruded material from the associated extruder. The invention also relates to allied techniques for finishing said extruded tubes.

Difficulties arise when connecting tubes, particularly synthetic plastic tubes, because as a rule one end of each tube fitting must be widened or, for example, if a thread has to be made in it, a thickening of the end is necessary. If in the first case the tube is widened out from its normal diameter to the increased diameter of a socket for the next tube, and annular corrugations are furthermore provided in the widened portion to accommodate sealing rings, then the widened portions have a smaller wall thickness than tube portions of normal diameter. This is most disadvantageous, as the portions with the larger diameter of ycourse require an increased wall thickness if they are .to be subjected to the same pressure as the unwidened portion rof the tube. Attempts have been made to overcome these difficulties by shrinking an annular tube, before the widening, over the corresponding tube end in the manner which is usual in armament production. Such a solution is however very unsatisfactory, as it is expensive and time-consuming in production and furthermore very accurate calculation is required if the stresses arising on the inner and outer tubes are to be uniformly distributed. As a rule, however, tolerances on synthetic plastic tubes are so large that the calculated value can certainly not be maintained.

Attempts have also been made to avoid the difficulty by accepting the thinner wall thickness at the sleeve ends of the tube and reducing the maximum pressure accordingly. This procedure, however, results in a considerable expenditure of material, as the total length of the tube, which is normally five meters or more, is overdimensioned.

The defects of the hitherto conventionally extruded tubes, are obviated in accordance with the invention in an extremely simple and rational manner, in that the tube string emerging from the extruder is upset at the desired distances while still in the deformable condition, in lengths corresponding to the widenings or thickening, to form a greater wall thickness, and that if requisite the widening and/or further treatment of the thickening is effected in known manner, or preferably by the method described later on, This process enables the existing difficulties to be overcome almost without any additional expenditure, as the upsetting can be effected very simply.

With thermoplastic material the thickening of the tube wall is advantageously effected before the end of complete polymerization.

In extruding tubes the tube string emerging from the extruder is advantageously guided by a cooled calibrating collar, in which the tube string is substantially finally polymerized. In the present invention the upsetting is advantageously effected in this collar. In this case the thickening obtained is on the inside. It may be produced, for example, by the extruder being temporarily stopped and the finished tube string being moved back one piece in the meanwhile. The upsetting ycan also be effected by the tube string being drawn off by a drawoff device following the extruder, at constant speed, and, for a short time during the emergence of the corresponding string portion from the extruder, the output of the latter being increased. The upsetting is, however, particularly advantageously effected by a periodic reduction of the speed of the draw-off device following the extruder, for the finished tube string.

If the thickening of the hollow tube string is provided outwardly, then this is advantageously upset over a calibra'ting mandrel and fully polymerized.

During the upsetting in a Calibrating collar, an overpressure, produced for example by compressed air being fed thereto, is advantageously maintained inside the tube string, which presses the tube against the calibrating collar. A special device for this is not necessary, because as a rule, the production of a smooth tube string is effected with an interior overpressure prevailing at least in the zone of the Calibrating collar.

After the upsetting, the finished tube string can be divided in the vicinity of the thickenings, after which these are widened in known manner to the desired diameter and desired sectional profile. The process according to the invention is advantageously effected by means of a known device, which comprises in sequence an extruder, possibly a calibrating device, preferably a cooling devi-ce such as a waterbath connected thereto, and finally a draw-off device. This draw-olf device is provided in accordance with the invention with an automatically acting device which periodically reduces the draw-off speed at the desired distances so that in the calibrating device during the period of reduced speed, a thickening of the tube string takes place. Said automatically acting device may be a mechanical one, as it is e.g. provided with automatical lathes, particularly multi-spindle automatics, or an electrical control circuit. Such devices are known to one skilled in the art. They are described e.g. in Dubbels Taschenbuch fr den Maschinenbau, vol. 2, page 627 (edited by Dr. Ing. F. Sass and Dipl. Ing. Ch. Bouch, Springer Verlag, Berlin, Gttingen and Heidelberg, 1958). The reduction of the draw-off speed may also be manually controlled; however, an automati-cal control device is preferable.

The Calibrating device may advantageously be a watercooled collar surrounding the `tube string emerging from the extruder.

Advantageously, a pipe for a pressure gas, preferably air, is provided, through which an overpressure is produced inside the portion of the tube string located within the collar, pressing this against the collar.

In the case of synthetic plastic tubes, increases in the internal diameter are also necessary when the tubes are to be joined together by means of spigot and socket arrangements, in which case one tube end is widened out to form a socket in which the unwidened end of another tube is inserted. The socket must then be provided with a corrugation which accommodates a sealing ring.

In this case the widenings have hitherto been produced by introducing the temporarily softened tube end into an outer female die determining the external form of thewidening and a pressure medium, air for example, being introduced into the tube end, by which pressure medium the softened tube wall is flexibly adapted to the inner surface of the die. Certainly in this way the outer forni is very accurately determined, but not the inner form,

which depends onV the plastic ow behavior of the tube material. However,fit is important to maintain ;accu-.

rately the inner shape of the widenings, as the sealing of the tube connections and also the guidance of the male tube endinthe socket depends decisively on the socket vdiameter and corrugation diameter and shape being accurately maintained.' Furthermore, it is essential that vthe wall thickness of thecorrugation inthe tube does not decrease too much in relation to 4the other tube wall thickness.

One object of the invention is therefore to make it possible to produce widenings, ofV ltherkind mentioned above,

atztube ends with 'theutmost precision of dimension of the inner surfaces of rthe `widened zoneparticularly in connection with the aforesaid tube connections. This Aand other problems are solvedby thel tube end being` drawn in plastic condition on a core which is variable in form and hasthe desired internal form of the Widenings,

lthe tube end being fixed over this, after which the core is: v removed from the tube end, a deformation of the core4 taking place, in particular ,acollapsing Obviously, in.v

accordance withvthe principle o frelativity in mechanics, the core may just as well be inserted in the tube end, or

both parts can be simultaneously moved one upon :the:n

other. Corresponding tests have shown that it issur-prisy ingly possible t-o push the tube end, rendered plastic,.over:` the widened core, substantially Without any jamming,LA

while the tube end again tapers behind the portion of the core again tapering towards the tube end. There are subf f stantially no upsettings of thefplastic tube end at all. The .Very slight upsetting, which may occur underV certain fcircumstances, may even be desirable, as by this the thinning of the wall, which happens as the diameter of the :tube end increases, is partially or wholly compensated.

The method in accordance with theinventi-onis ad?? vantageously carried out in such a way that the widening zones of -the tube tapering towards the tube end, are exiblyadapted to the coreY and/or are calibrated, by means of an outwardly engagingy device. In this way it is further possible to make any desired correction to the Ywallt thickness. Furthermore, `the endffaee of the tube can Lebe conjointly formed, so that it lies accurately in a plane normal to the axis of the tube. It may be given any desired;

profile and, for example, may be rounded.

The tube end is advantageously pushed onto the corel by a sliding means such as, preferably, oil.

The core is advantageously heated before the tube end:

is pushed on, in order to prevent any premature solidication of the. tube end.

The-method according to the invention makes it pos- -t sible to produce connecting sockets for tube ends with a,

degree of accuracy in measurement and shape not hitherto known.

A device for carrying out the method for widening is characterized bythe inclusion of a holding device for the Y tube to be worked, a variable-form core arranged axially -V in front of the center of this holding device, a device Afor axial displacement of the core and tube holding device in relation to one another and also a device to bring the core to a shape in which it can be drawn from the formed tube end. K

There is advantageously provided, for exterior calibration and/or exible adaptation of the tube end to the core, a cylinder which israxially'movableover the tube end and is given a profile corresponding to it. i Advantageously hydraulic moving devices are provided for the tube holding device, the profiled cylinder andthe deforming of the core.

The core advantageously comprises, at least in the zone of the Widening or widenings narrowing towards theY tube end, a multiplicity of segments, Which'are axially and,

radially movable in Vrelation to one another. The `segments advantageously consist of two groups of segments, which intermesh in the manner of gear. teeth,` in which connection,.viewed in a plane normal to the axis of the',

ably' articulated. Y

The segmentsr` not narrowing in width'towards the. axis are advantageously arranged. onia core member; con.

jointly forming if requisite the. tube, widenings; land displaceableaxially toxthethickening, 'movable ini planes radialtofthe axis, andpreferablylswivelably articulated.

Stops are advantageously provided preferablyV at :the

thickening and the corey member` whichIrestr-ict the mobility of the segments outwards.

Thereis advantageously providedrinside vthe core, andr preferably displaceably onrthe rod,fan,` axially displaceablesegment control and holdingmember. In the movedin position in the core,.the controland holding member r presses, by corresponding surfaces, -the segments into their radially extreme position, while in the moved-out position, it leaves the .segments yfreel for .inward movements.

The. .control and Iholding member .-is advantageously providedwith stops,:which swivelfthe segments atV the core member? inwards during` the outward travel. of -the COTE.

The control and holding vmemberriis advantageously!v provided` with stops, preferablyjengaging the segments of the core member, which stops entrain the.y corek member during outward travel.

A member, preferably a bar arranged inthe rod, is advantageously provided co-axially With'the'rod, for moving:

the control and holding-member.r

The bar is advantageously connected with the .control and holding member by means of fingers engaging through x recesses of -the rod. Y

The said thickening is advantageously a body widening f the tube 4to form the socket, which Iis -externally complemented by the segments sitting on it, while :the .totality of the segments have an annular beading extending over; their periphery, which zproduces a peripheralfcorrugation in I the sleeve. z

The profiled, cylinderl is advantageously displaceablelaxially on athe rod.`

A cooling device-for` the widenedtube end, preferably Y a trickle devic'e,is advantageously provided `surrounding a the core at a distance fromit.Y

A-heating device for heating thesynthetic plastic mate-V rial'to the softening temperature .is advantageously prof vided.

Specific embodiments of the invention-will'V now Tbe describedby ways of example with reference to the accompanying diagrammatic drawings, in which:-

FIGUREtl illustrates'the upsettingof a tube str-ing,

FIGURE 2 shows on a larger scale thev portion of the i tube-stringlocated `in:the Calibrating `collar ,during the thickening process,

' FIGURES Iis an exaggeratedrepresentation, showing in the upper half the socket end of a synthetic plastic tube as in known art, andy FIGURE `4 shows inthe lower half a socket end produced in=accordance with the present invention,

FIGURES shows a device, part-ly in section, in accord ance with the invention for widening tube ends, afterl the wideningofthe tube end and rbefore ythe disengagement of they core and tube end, l'

FIGURE! 6 shows a `section taken online III-III'in;

FIGURE 5,

FIGURE? shows the device of vFIGUR-E? 6 after the disengagement ofthe core [and tubey end,

FIGURE 8 showsv on enlarged scale a longitudinal sec"y tionthrough the core of they device shown in 'FIGURES 5 Ito 7, located in the lfinished widened tube end, in which connection the calibrating and flexible adaptation cylinder is still mounted over the tube end, this section corresponding to section line IV-IV of FIGURE 9,

FIGURE 9 shows Ia section taken on line V-V in FIGURE 9, and

FIGURE shows a section similar to FIGURE 9, but with the core collapsed so that the tube end can be withdrawn 4from the core.

There will now be described in .connection with FIG URES 1 to 3, the first step of the production of synthe-tic .plastic tubes with ends widened to 4form a socket, the tube wal-l being thickened before the widening.

In FIGURE 1 is diagrammatically 'represen-ted the end face of an extruder 71, in whose aperture there is located a core 72 so that out of the aperture there is pressed a round synthetic plastic tube 79 consisting of, for example, polyvinyl chloride. The wall thickness of the tube 79 is determined by the difference in diameter between the extruder aperture and the core 72. To the extruder lis connected a hollow calibrating collar 73, in which cool water circulates.

At a distance yfrom the calibrating collar 73 is provided a cooling water bath 74 which cools the tinished tube emerging Ifrom `the calibrating collar 73 so that this tube can be gripped, without being damaged, by a draw-off device which works -at the same speed as that at which the tube is pressed out of the extruder. The draw-off device consists, in the embodiment shown, of radially spaced rollers 75, which convey the tube further on. According `to the invention there is `provided a conventional drive 76, for At-he draw-olf device, including an automatic control device of conventional-type, which decreases t-he speed of the draw-oli intermittently.

At predetermined times, the draw-off speed is reduced by the control device by a lgiven percentage such as, for example, As however the quantity ofthe synthetic plastic material emerging from the extruder is not decreased, during operation at reduced drawn-off speed there is produced, Iby the heaping up of material (upsetting) directly followng the discharge aperture of the extruder, a tubular -section with a correspondingly increased vwall thickness, .as is more clearly shown in FIGURE 2. If the draw-off device now begins to run at normal speed again, there then follows, adjacent the tubular section with increased wall thickness, a tube portion of normall wall thickness.

In the vicinity of the calibrating collar 73, there may be provided a device which, for example by means of compressed air fed through the .core 72, maintains an overpressure inside the tube string produced.

To show an example of the above method, the following data are given.

A tube polyvinyl chloride with an external diameter of 100 millimeters (mm.) and an internal diameter of 80 mm. is to be extruded. The polyvinyl chloride has a tensi-le strength of 5 to 5.5 kilogram per square millimeter. The wall thickness ofthe tube, normally 10 mm., shall after 6 meters be increased to 20 mm. on a length of 0.5 meter. The thickening of the wall shall be on t-he inside of the tube wall. The extrusion speed and the draw-oli speed are 1.5 meters per minute during the extrusion of the normal ytube length. rl`he extr'uder aperture is a usual one lfor extruding tubes of the above mentioned dimensions. The temperature at the extruding aperture is also a usual one, preferably between 120 and 140 C. After extruding of 6 meters tube length the draw-off speed of the draw-off device is reduced to 0.844 meter per minute without changing the ext-rusion speed. Now the ext-Puder will deliver a part of the tube string with still an external diameter of 100 mm. T-he internal diameter of this part however will be 60 mm. After extrusion of a length of 0.5 meter of a so walled tube the draw-off speed again is increased to 1.5 meters per minute. Now the thickly I-t is of importance in the process in accordance with the invention that in treating t-he synthetic plastic material the production of the zone of increased wall thickness be eifected before the synthetic plastic material, for example, polyvinyl chloride, polyethylene lor other thermoplastic material, has been completely polymerized. If the upsetting is eifected after iinal polymerization with a renewed heating of the corresponding tube portion, this has the disadvantage tha-t, with a subsequent heat-ing, the upset portion has a tendency to assume again the shape which it had before the upsetting. r

T-he tube string produced in the manner described above is now cut into individual tube components each having a thickening -at the end. The upset ends are then brought into a female die, heat being applied, if for example they are to be widened to socket ends of increased diameter, in which `female die they are widened in known manner to the desired diameter and the desired form. In this way there can be produced widened socket ends into which tube ends o-f nor-mal diameter can be inserted. In the course of the widening process there may be lproduced during the same operational sequence `an annular groove in the socket end, which groove accommodates a sealing ring. A socket end 77 thus produced is Arepresented in the lower half of FIGURE 3, while its upper half shows a similar socket end 78 of known type.

In a similar way the tube end can also be widened for example in a female die provided with a female thread, so that the tube end has a reinforced end with a male thread. The dimensions given to the upset portion and the die must be such that after the working in the die the bore of the tube in the vicinity of the thickened end is substantially equal to the normal diameter of the tube.

In a similar way it is also possible to thread a widened tube end by inserting it in an inner male die.

The upsetting process described is particularly suitable for working synthetic plastic material like polyvinylc'hloride or polyethylene.

The widening of a tube end for an insert socket will now be described with reference to FIGURES 6 to ll.

In FIGURES 5 to 7 is shown a holding device 1 for a tube to be widened at its end, and also a core 2, a calibrating and flexible-adaptation cylinder 3 and a movement device 4 for the core and the cylinder.

The holding device comprises chucking jaws 6, axially movable and supported on rods 5, which chucking jaws can grip the tube 8 under the control of a hydraulically actwated chucking cylinder 7. The two chucking jaws 6 are supported by plates 9 and 10, which are pivoted on the spindle 11. For axial displacement of the chucking jaws and the tube held thereby, there is provided a hydraulic cylinder 12 which engages by means of a rod 13 against the plates 9 of the chucking jaws.

' A rod 15 xed to the device frame 14 carries the core 2. For collapsing the core 2 there is used a hydraulic cylinder 18, which by means of a bar guided inside the rod 15, collapses the core, in a manner which will be hereinafter described, to such an extent that the widened tube end can be drawn off it. The calibrating and flexible adaptation cylinder 3 is guided on the rod 15 and is moved axially by the hydraulic cylinder 16. For this purpose there is mounted on the thrust rod 17 of the hydraulic cylinder 16 a disc 19, which engages by means of two rods 20 against the calibrating and flexible adaptation cylinder 3.

In the embodiment shown, the tube end` is to be widened to form a socket which hasan annular corrugation 21!` (FIG. For this purposethe device is rst'brought into a position inrwhich the rcore 2 is closed, while the cylinder 3 however 'has travelled yto the left into the posi- Y tion shown in FIGURE 7. The tubeS to be widened is chucked in the chucking device after its end is first of al'l heated by the heating device 22, which is only indicated diagrammatically, to the thermoplastic softening tempera-` ture of the tube 8 Vconsisting for example of polyvinylchloride. The core is previously externally lubricated with a lubricant, for example, oil. The tube is now moved on the core, the end of the tube, whose wall thickness has f already been thickened, being pushed over the core.: As the plastic material of the tube .end has a certain amount' of elasticity,.it passesV over the annular beading 23 of the` core and flexibly adapts itself to the core 2, narrowing to the left of the annular beading. The cylinderV 3 is nowV moved onto the tube end in such a way that it fits` with its correspondingly formed inner surface the portion of the tube located to the left of the corrugationf21 produced in the tube end, and if requisite exibly adapts itself to the core. This exible adaptation primarily insures that the zone of the internal surface of the socket, indicated inFIGURE 10 by x, .is itself in a markedly curved form, accurately and flexibly adapted to the core.L

When the tube end has receivedthe desired widening( and profiling, then by means of the diagrammatically in-V dicated cooling device 24 (FIG. 7) consisting of a trickle? installation, the portion of the formed tube end not covered by the cylinder 3 is sprayed and further solidied by the resulting cooling.V Then the cylinder 3 is moved to the left and the part of the tube end hitherto covered by it is likewise solidified by the spraying. Finally, by means of the hydraulic cylinder 18 the core is collapsed in a manner hereinafter described so that the tube can be. ,f

drawn from the core by means of the hydraulic cylindery 12. Then the next tube end can be widened and profiled in the same manner.

In the following, the construction and mode of opera-l tion of the core will be described in connection with FIGURES 8 to 10.

In FIGURE 8 is shown the cylinder 3, in order that its interior-may be better understood. It is provided with threaded holes 25, in which the rodsV 20 are engaged.

The core, as already explained above, is carried by. the

rod 15.' At the end of the rod 15, ya core thickening 27 33, surrounding the .nut 28, into the zone of the tube 8 s which is notV to be widened, collar 33 serving for guide purposes. The tube S Vis shown in FIGURES 8 to l0 in the finished kwidened condition. The base body 30 has on its periphery, regularly distributed at a distance apart fromy one another, siX release or tripping devices 34 (FIGUREl 10) in which segments 35 are supported so as to be able to swivel round spindles 36.- These segments 35have, as can be seen in FIGURE l0, wedge-shaped proles in the geometrical sense in planes normal to the axis of the cores. In particular they only have this profile in the zone in which they come into contact with the segments 37;vv In their portion further to the right in FIGURES Sand 9 for production reasons they have rectangular profiles, which facilitates their bearing on the release devices 34 of the base body 30.

A control and holding cylinder 41 provided with release devices 39 and 40 associated with each of the six seg.- ments 37 is supported axially displaceably on the rod .15 by means of the bar 16. The connection of the bar 16 With the control and holding cylinder 41 is effected by means of a pin 42 which projects through elongated slots 43 in the rod 15.v By means of its surfaces 44, the cylin-f surfaces of the segments 35i as the core moves together.

The Ycore member 47 consists of an annular body 48;l

which partly projectsbya outer collar 49 :in relation to a second annularf body 50 likewise associated withfthe core member. ,nectedby screws 51. Thetannularbody 50'has six krelease devices 52.

surfaces 54 extending parallel to oneianother; Vso that they can still be swiveled inwards while they are ybetween the segments 35.- Their .extreme positionis determined by the application of their surfaces; 35 :to the correspondingY surfaces` of the. control'and-holding member andalso by application of their rsurfaces `56'1to;corresponding sur*- faces of the base -bodyt30.. The segments 37 are provided .Y with fingers 58,'iwhich can .cooperateA withY corresponding surfaces 59 fofithe release devices: 39 .of the control and holding cylinder341. There willnow ybe described they movement of the core vbetween thei positionfshown in FIGURES and the posi tionl shown in yFIGURE 10. For this purpose they bar 16'V and the control and holding cylinder 41 connected .with it f are moved lto the left, asfar as is permitted by the axial slots 43 in the .rod 15. With this'movement the surface 59y -rst abuts against the finger 58 vof the segment 37 and; swings this inwards into theLpositionishown in FIGURE 10.'y Asy the.V member 41 slides. on -to the left the; surfaces of the segments; 37 cooperating with the surfaces. 56. finally come into engagement with the surfaces 60 of the' release devices 40 in theV position shown in FIGURE 10. Then the member 41.t also entrains,v by engaging against the segments 37,#the core member 47 whichis'supported .so as to be able to move yfreely and axially on the periphery of the control and holding cylinder 41. The segments 37' swiveled inwards; vas described.aboveA no longer project into corrugation 21* so that they: can be withdrawn fromv the tube end. With the ftravelto the left ofthe controlr and holding cylinder 41 v,the swiveling inwards has uncovered to its surface 44l to free the segments 35, so that these,

when the tube is withdrawn fromithe core,.can be swiveled inwardly under they influence of the tube wall, into the position shown .in FIGURE7 10, as the tube is withdrawm After the tube is drawn off, the :control and holding member 41 is again moved, by means of the bar 16, to the right [whereby it moves the segments-35 back again to their outwardl positions.; With `further ,displacement of the.

member: 41ifitowards1the right, the surfaces 65 of the release devices 40 pivot the segments 37 such thatsuifaces 55 slideon the surfaces 66. AsY the controland holdingl memberfwhen the'coresections have moved-together,L presses with Iring 67 against the annular body 48, the whole Y core is firmly held .togethelm` Attention isinvited to the kfact that Aelements 35 and 37 j cooperatively constitute ,a ,male die having a continuous surface. Y This male die.is,further,1col1apsible. 'Ihis fea# Y ture is advantageously effected by interdigitating elements between the elements 351 after which the.` latter can be o collapsed.

It'should be noted in further accordance with the invention that theA core can be heated before the. application of the tube end, in order to prevent a premature setting of the latter.

Theiinvention is not restricted to the examples described, but is in fact susceptible of :variation Within the scope of the following claims. Y Y

The :annular :bodies: 48 and 50 .are conf.

Ineach of these release rdelvicesfa segment. 37 is supported sor as to swivel'aroundthe spindle 53'.`=` The segment 37, as kcan beseen in FIGURE 8,;haslateral.

What is claimed is:

1. A process for the production of plastic tubes which have at least at one end thereof an increased wall thickness for a predetermined length, said process comprising continuously advancing plastic material through an extruder to produce a continuous extruded cylinder, cooling the extruded cylinder as it is discharged from the extruder whereby the plastic material is hardened thereat,

,engaging the thus cooled cylinder to draw the sarne through the extruder and rpast the region where the cylinder is cooled, periodically increasing the ratio of the speed at which the material is fed to the extruder relative to the speed at which the cylinder is drawn from the extruder to upset the tube where it is discharged from the extruder to form periodic increases in thickness in the cylinder and dividing the cylinder thus formed with the periodic increases in thickness to produce tubes which have increased wall thickness at least at one end thereof.

2. A process as claimed in claim 1 wherein said ratio is periodically increased to values greater than 1 by reducing the speed at which the cylinder is drawn from the extruder.

3. A process as claimed in claim 1 wherein said ratio of speeds is periodically reduced for a time period in which the predetermined length of increased wall thickness is produced.

4. A process as claimed in claim 1 comprising widening the tubes at the ends of increased thickness to form sockets adapted for connection with pipes.

5. A process for the production of plastic tube members having at least at one end thereof for a predetermined length, an increased wall thickness, said process comprising continuously extruding from an extruder aperture a plastic tube, solidifying the plastic tube by cooling, conveying the cooled plastic tube by a conveying device acting on the solidified tube, guiding the tube as it emerges from the extruder aperture through a calibrating collar and cooling the tube thereat, increasing at intervals, which correspond to the desired length of increased wall thickness the ratio of the speed with which the tube is extruded from the extruder aperture, relative to the speed with which the conveying device conveys away the solidified tube to a value which is greater than l, whereby the non-solidified zone of the tube is upset to a greater wall thickness during said intervals in the Calibrating collar, and dividing the tube into tube members at said zones of increased thickness whereby said members will have at least at one end thereof an increased Wall thickness.

6. A process as claimed in claim 5 wherein said ratio of speeds is increased by reducing the speed at which the tube is conveyed by the conveying device.

7. A process as claimed in claim 5 comprising widening the tube members at the ends of increased thickness to form sockets adapted for connection with pipes.

8. A process for the production of plastic tubes which have at least at one end thereof an increased wall thickness for a predetermined length, said process comprising continuously advancing plastic material through an extruder to produce a continuously extruded cylinder, partially cooling the cylinder in a first cooling stage located immediately beyond the extruder, completely cooling the cylinder in a second stage at a distance from the rst stage whereby the cylinder is completely solidied, engaging the thus cooled cylinder to draw the same from the extruder through the cooling stages, applying pressure to the interior of the cylinder to cause the cylinder to peripherally engage a surrounding collar at the first cooling stage whereby said cylinder assumes a substantially constant outer diameter at said first stage and is at least partially solidified thereat, periodically increasing the ratio of the speed at which the material is fed to the extruder relative to the speed at which the cylinder is drawn from the extruder to form periodic increases in thickness of the cylinder at the collar whereat the outer diameter remains constant while the inner diameter of the cylinder is reduced, and dividing the cylinder thus formed with the periodic increases in thickness to produce tubes which have increased wall thickness at least at one end thereof.

9. A process as claimed in claim 8 wherein said ratio of speeds is :periodically increased by decreasing the speed at which the cylinder is drawn from the extruder.

10. A process as claimed in claim 8 wherein said ratio i of speeds is periodically reduced for a time period in which the predetermined length of increased wall thickness is produced.

11. A process as claimed in claim 8 comprising widening the tubes at the ends of increased thickness to form sockets adapted for connection with pipes.

References Cited by the Examiner UNITED STATES PATENTS 2,282,282 5/1942 Hamlan 264--150 2,512,844 6/1950 Weber 18-14 2,746,839 5/1956 Terry et al. 264-167 2,948,919 8/1960 Matthews 264-150 3,152,202 10/1964 Murphy 264--209 ROBERT F. WHITE, Primary Examiner.

M. H. ROSEN, M. R. DOWLING, Assistant Examiners. 

1. A PROCESS FOR THE PRODUCTION OF PLASTIC TUBES WHICH HAVE AT LEAST AT ONE END THEREOF AN INCREASED WALL THICKNESS FOR A PREDETERMINED LENGTH, SAIDROCESS COMPRISING CONTINUOUSLY ADVANCING PLASTIC MATERIAL THROUGH AN EXTRUDER TO PRODUCE A CONTINUOUS EXTRUDED CYLINDER, COOLING THE EXTRUDED CYLINDER AS IT IS DISCHARGED FROM THE EXTRUDER WHEREBY THE PLASTIC MATERIAL IS HARDENED THEREAT, ENGAGING THE THUS COOLED CYLINDER TO DRAW THE SAME THROUGH THE EXTRUDER AND PAST THE REGION WHERE THE CYLINDER IS COLLED, PERIODICALLY INCREASING THE RATIO OF THE SPEED AT WHICH THE MATERIAL IS FED TO THE EXTRUDER RELATIVE TO THE SPEED AT WHICH THE CYLINDER IS DRAWN FROM THE EXTRUDER TO UPSET THE TUBE WHERE IT IS DISCHARGED FROM THE EXTRUDER TO FORM PERIODIC INCREASES IN THICKNESS IN THE CYLINDER AND DIVIDING THE CYLINDER THUS FORMED WITH THE PERIODIC INCREASES IN THICKNESS TO PRODUCE TUBES WHICH HAVE INCREASED WALL THICKNESS AT LEAST AT ONE END THEREOF. 